Positive feed tools, such as but not limited to feed drills, are conventionally known for performing operations on workpieces formed of substances such as steel, aluminum, titanium, and composites. Positive feed tools include a tool feed mechanism that feeds a bit into a work piece. Conventional applications for positive feed tools include, among other applications, drilling holes in various parts of aircraft.
Positive feed tools generally include a motor configured to drive a spindle. The spindle may be rotated, and may advance a predetermined amount per revolution. The spindle is designed to move in an advance direction towards a workpiece, and a retract direction away from the workpiece.
Tools are designed to initiate a shift in the spindle from moving in the advance direction to moving in the retract direction. Typical methods for initiating the shift from advance to retract are mechanical cam levers or pneumatic pistons actuated by a pneumatic limit signal. Reliability of the operation of these mechanisms is vital for the operation of the tool. Failure of the mechanisms at this point may result in a disabled tool stuck with the spindle in the forward position. This can cause damage to the workpiece and/or the tool.